China executed three knife attackers Tuesday for their role in killing 31 people at a train station in the southwest city of Kunming last year.

According to Reuters, Iskandar Ehet, Turgun Tohtunyaz, and Hasayn Muhammad were from the far western region of Xinjiang, home to the Muslim Uyghur minority group. They were accused of leading a separatist terrorist organization by the Kunming Intermediate People's Court.

Convicted attacker Patigul Tohti, who was pregnant when arrested, received a life sentence in prison.

The attack was staged on March 1, 2014, and police shot and killed four assailants during the clash. 141 people were injured during the incident.

The Chinese government restricts certain aspects of the Uyghur religion and culture, and many have rebelled against the sanctions over the years.

"China's use of the death penalty as a political tool does not address the root of the problem," said Dilxat Raxit, a spokesman for the exiled World Uyghur Congress. He says the defendants were denied a fair trial.

"China continues to make use of this incident to incite discrimination against Uyghurs."